Various toys having combined rotational motion about a horizontal axis and a translational motion in a vertical direction are known. One type of such toy is commonly referred to as a yo-yo. This toy has also been referred to as a return top; quiz; Prince of Wales' toy; disc; Coblenz; Incroyable; Bandalore; or emigrette. According to the Patent Office classification, a yo-yo is a tethered aerial top. A conventional yo-yo consists of a single axle having two parallel positioned discs centrally connected to the axle. A string is connected to the axle between the discs at one end and is held in the use's hand at the other end. The string is wrapped around the axle by the user and the yo-yo is then forced downward. Upon being forced downward, the string unwinds and provides a rotational momentum to the discs. Once the string has been completely unwound, the rotational momentum of the discs continues to exist, thus causing the string to be rewound around the axle as it travels upward vertically toward the user's hand. The conventional structure of this yo-yo is disclosed within U.S. Pat. No. 3,263,361 to Bowden, and U.S. Pat. No. 3,256,635 to Radovan.
In another variation of the yo-yo, the string is not actually secured to, or anchored to, the axle; rather, it is looped about the axle somewhat loosely, allowing the yo-yo body to spin freely in the looped string. Such rotational motion of a yo-yo, unaccompanied by translational motion along the string direction, is referred to as "sleeping". The sleeping yo-yo can be withdrawn from its sleep by jerking the string, or alternatively, by relaxing the tension in the string. The conventional sleeper-type yo-yo is discussed in the specification of Stivers and Ennis, U.S. Pat. No. 2,629,202. Another mechanism for allowing a yo-yo to sleep, but which does not involve a looped string, is discussed in Isaacson, U.S. Pat. No. 3,175,326. Isaacson's device involves an axle which is rotatably supported in a ballbearing system.
The conventional yo-yo structure as described above has achieved tremendous success in the past as an entertaining toy. Furthermore, certain modifications of that conventional yo-yo such as that disclosed within Bowden or Isaacson may have achieved success as entertaining toys. However, the conventional yo-yo structure has a pronounced limitation when used by inexperienced or younger operators. The limitation is apparent to even the most casual observer and resides in the ability to maintain the balance or equilibrium of the toy during use. The inability of the inexperienced user to maintain this balance results in a wobbling and precessional motion of the yo-yo during operation. The operator loses control of the yo-yo when the balance of the toy is disturbed, thus causing the yo-yo to slow its rotational motion and thereby lose its ability to maintain vertical translational motion.
In the context of this specification, the term "stability of yo-yo" is intended to mean the tendency of the yo-yo axle to remain in horizontal alignment during an up-down translational motion of the yo-yo body, and its tendency to return to this alignment if it is displaced therefrom by some means. The term "stability of yo-yo" also refers to the facility with which proper yo-yo operation can be re-established after it experiences wobbling or precessional rotation; the greater the stability of the yo-yo, the easier it is to re-establish proper operation after it encounters difficulty.